JP3110464B2 - Heavy metal cation scavengers containing silicate, aluminosilicate or carbonate type compounds - Google Patents

Abstract

PCT No. PCT/FR95/00557 Sec. 371 Date May 20, 1997 Sec. 102(e) Date May 20, 1997 PCT Filed Apr. 28, 1995 PCT Pub. No. WO95/29875 PCT Pub. Date Nov. 9, 1995An agent for recovering heavy metal cations from an aqueous effluent, including a silicate or aluminosilicate type compound, e.g. an alkali metal silicate or aluminosilicate, and a carbonate type compound, e.g. an alkali metal carbonate, and preferably a carrier such as a lay. The agent may also form a cation stabilizer. Said agent is useful for removing or stabilizing heavy metal cations in the water used for cleaning flue gases from waste incineration, particularly household refuse and industrial waste incineration.

Description

The present invention relates to a scavenger (remover) for heavy metal cations contained in a medium, especially an aqueous effluent.

Waste incineration is subject to very strict regulations. In particular, regulations on the emission of heavy metals to the environment are strict. Cleaning (purification) of fumes in households and industrial waste incineration plants, especially incineration plants for sulfur-containing wastes such as waste sulfuric acid
Is a medium containing heavy metals. Similarly, certain soils are contaminated by the presence of such heavy metal ions.

Thus, conventional methods of removing heavy metals from sewage obtained from the cleaning (purification) of fumes generated during the incineration of wastes such as household refuse use lime to perform basic precipitation and then remove sulfur. The base precipitant acts in an auxiliary manner. Separation is performed by decanting thereafter, and the separability is generally further improved by a flocculant.

 However, this method has some disadvantages.

In particular, very large amounts of sludge are generated by sedimentation using lime. After filtration and compaction into cake form, the sludge must be disposed of at a specific disposal site.

In addition, the use of organic materials, such as sulfur-based precipitants and flocculants, can be harmful to the disposal site because at least part of it remains in the cake (generating reducing gas over time). And deteriorate).

Finally, the resulting sludge composition is difficult to stabilize (or immobilize) with current technology. If a large amount of calcium is present in the sludge, stabilization treatment (or immobilization treatment) such as vitrification is greatly inhibited. However, future regulations on the final storage of a particular waste will require that the cake be stabilized (or immobilized) before being transported to such storage or disposal sites to sufficiently reduce leaching from this type of waste. Request.

An object of the present invention is to provide a means for efficiently capturing (or removing) heavy metal cations, which does not have the above-mentioned disadvantages.

For this purpose, the present invention provides a novel treating agent for capturing or removing heavy metal ions present in a medium. The treating agent is an inorganic product containing at least one compound of the silicate or aluminosilicate type, at least one compound of the carbonate type and, if necessary, at least one carrier, preferably clay.

The present invention also provides a heavy metal cation stabilizer (immobilizing agent) containing the above-mentioned scavenger or remover.

Applicants have surprisingly found that the use of a scavenger or scavenger as defined above makes it possible to remove heavy metal cations from a medium containing heavy metal cations very efficiently; The improved separation and decanting of the spent liquid, the ability to stabilize this sludge, i.e. the ability to suppress leaching, and the residual calcium content in the sediment obtained by the above-mentioned conventional method, It has also been found that an extremely low residual calcium can be obtained, which is an advantageous effect.

One subject of the present invention is a scavenger or remover for heavy metal cations contained in the medium, comprising at least one silicate or aluminosilicate type compound (hereinafter referred to as compound A); At least one carbonate type compound (hereinafter, referred to as compound B) is a constituent element.

Here, the heavy metal cation is particularly 2 or more, preferably 2 or more.
Metal ions having a valence of, in particular, antimony, arsenic, bismuth, cadmium, chromium, cobalt, copper,
Includes ions of metals such as tin, magnesium, molybdenum, nickel, gold, lead, thallium, tungsten, zinc, aluminum, iron, and actinides.

Heavy metal cations to which the present invention is particularly intended are cadmium, chromium, copper, tin, nickel, lead, thallium, zinc, aluminum, and iron.

 The medium here is preferably a liquid medium.

This medium is obtained from the cleaning of aqueous effluents (waste liquors), in particular the soil from water and heavy metals, obtained from the cleaning (purification) of fumes from household waste, industrial waste or hospital waste incineration plants. It consists of water and aqueous waste liquid used for surface treatment.

The inorganic product of the present invention that captures or removes heavy metal cations in a medium therefore comprises at least one active principal (ie, a precipitant) consisting of at least one compound A and at least one compound B.

Compound A is preferably an alkali metal (particularly sodium or potassium) silicate or aluminosilicate.

 Compound A is advantageously sodium silicate.

Sodium silicate generally has a SiO ₂ / Na ₂ O molar ratio of 0.5 to 3.8
In the range.

Compound B is preferably a carbonate of an alkali metal, or hydrotalcite and daussonite (da
wsonaite).

Hydrotalcite is basic magnesium aluminum carbonate. Daisonite is a basic sodium aluminum silicate.

Compound B is advantageously an alkali metal (particularly sodium) carbonate.

The molar ratio between compound B and compound A can vary over a fairly wide range, but is generally 0.05 to 1 in terms of CO ₃ ²⁻ / SiO ₂ molar ratio.
0, preferably in the range of 0.33 to 3.

 The treating agents according to the invention can be in powder or granular form.

According to a preferred embodiment of the present invention, the treating agent of the present invention may have at least one carrier (substrate).

In this case, the treating agent of the present invention comprises at least one active main agent (precipitant) comprising at least one compound A and at least one compound B.
And at least one carrier (substrate), preferably a clay, and a composite product.

 This composite (inorganic) product generally has a powder form.

In this case, a carrier that is a clay is included in the treatment according to the present invention.

The carrier contained in the treating agent according to the present invention may be a natural product or a synthetic product.

Clay used in the present invention is a high Al ₂ O ₃ content, for example it is advantageous to have a 20-40%.

According to the invention, it is preferred to have a lamella structure or a phyllosilicate structure (multilayer).

Clays selected from kaolinite and serpentine can be used.

The clay may also be selected from the group of montmorillonite, bentonite (especially alkaline), talc, and mica.

The selected clay belongs to one of these two groups.

Further, it may have a chlorite type structure.

Embodiments of the treatment according to the invention broadly include montmorillonite.

In a preferred embodiment of the present invention, the content of the carrier, especially clay, in the treating agent is generally 10 to 80% by weight, preferably 10 to 30% by weight, based on the total amount of the treating agent.

The treating agent of the present invention generally contains 1 to 20% by weight of water.
This water content can be determined by calcining at 350 ° C. for 6 hours and measuring the weight loss.

The treating agent of the present invention has a weight average particle size of 15 to 100 μm, preferably 20 to 75 μm.

The treating agent of the present invention can be produced by an appropriate method.

According to a first aspect of the present invention, the aqueous solution of compound A is mixed in a first step with an aqueous solution of compound B (which can be pre-adjusted to the same pH as compound A), or solid compound B Mix with.

After stirring, the solution obtained using this mixture is
Drying, for example, by a flash method or, preferably, by a spray method.

According to the second aspect of the present invention, a mixture obtained by adding an aqueous solution of compound A to solid compound B, or conversely, a mixture obtained by adding an aqueous solution of compound B to solid compound A is required. Then, after further stirring, the mixture is subjected to a granulation treatment using any known granulator, for example, a plate-shaped granulator. This granulation is usually completed by a subsequent drying step, for example fluid bed drying.

 The pH of the aqueous solution of Compound A is usually 10-14.

When compound A is sodium silicate, SiO ₂ / N
a ₂ O molar ratio of sodium silicate of 0.5 to 3.8 is used, SiO 2
_The silicate concentration represented by ₂ is 0.1 to 10 mol /, for example, 0.2 to 10
It is an amount of 8 mol /.

When compound B is sodium carbonate, Na ₂ CO ₃ is generally used.
Is 0.1 to 5 mol /, for example, 0.2 to 3
It is used in an amount of mol /.

The stirring operation is generally performed for 5 to 45 minutes, for example, 10 to 25 minutes.

The drying step is usually performed at a temperature of about 40-500 ° C using a suitable device.

Drying is particularly performed by the spray method in the first embodiment.

For this purpose, a suitable atomizer, such as a Buchi atomizer, a turbine atomizer, a nozzle atomizer, a liquid pressure atomizer, or a fluid atomizer can be used.

Inlet temperature is generally about 230-250 for Buchi type atomizer
° C, about 450 ° C for the turbine atomizer and the nozzle atomizer, and the outlet temperature is generally about 110 to 140 ° C for the Buchi type atomizer, and about 125 ° C for the turbine atomizer and the nozzle atomizer.

For drying purposes, an apparatus (flash type) having an inlet temperature of about 500 ° C. and an outlet temperature of about 150 ° C. as described in US Pat. No. 4970030 can also be used.

The drying step may be performed in a fluidized bed particularly in the second embodiment.

If it is desired to produce a treating agent according to the invention containing a carrier, in particular clay, according to the first form briefly described above, the carrier can be treated with an aqueous solution of compound A and a base (for example sodium hydroxide). ) Is preferably added to an aqueous solution of compound B or a mixture with solid compound B which has been adjusted to the same pH as the aqueous solution of compound A in advance. Usually, this addition is carried out with stirring of the mixture before, during and after the addition of the carrier.

Similarly, according to the second aspect described above, a carrier (eg, clay) previously charged to the granulator, usually with stirring.
, A mixture of an aqueous solution of the compound A and an aqueous solution of the compound B is added, or the compound A (or the compound B) is used in the first step.
Is added, and an aqueous solution of compound B (or compound A) is added at a later stage. Granulation is performed, for example, using a plate granulator, and then the process is preferably completed by drying, preferably by fluid bed drying.

In these two forms, upon completion of production, a product is obtained in which the active principle is advantageously intimately bound to the carrier.

The at least one treating agent of the present invention is used to remove heavy metal cations from media containing heavy metal cations, especially liquid effluents (or solutions), more specifically aqueous effluents (or aqueous solutions). The method is performed as follows.

The treatment agent of the invention is introduced into the liquid effluent to be treated with stirring. The embroidery pH of the suspension containing the treating agent is preferably between 7 and 12 or 7 by addition of a base or acid.
Adjusted to a value in the range of ~ 12. This pH is more particularly about 9 or adjusted to this value. The final pH depends on the amount of treatment agent of the invention introduced to the liquid effluent to be treated and the initial pH of the liquid effluent. The stirring is continued for, for example, 5 to 60 minutes. The suspension is then left (sedimented) at room temperature for a period of time, generally 0.5 to 24 hours. The sedimentation time can be reduced by using a known sedimentation promoting method. The precipitate formed, ie, the treating agent of the present invention incorporating the heavy metal cations, is separated by decanting, filtering, and / or centrifuging the suspension.

In general, the medium to be treated is 0.5 to 600, especially if it is a liquid effluent, especially an aqueous effluent or aqueous solution.
It contains 0 mg /, for example 1-1000 mg /, especially 2-100 mg / of heavy metal cations.

The amount of the treatment agent according to the invention added to the medium to be treated is such that the molar ratio of (SiO ₂ + CO ₃ ²⁻ ) / (cations present in the medium to be treated) is 0.7-2.5, For example, 1.0
It is an amount such that it is ~ 2.2, especially 1.1-1.9. The cations present in the medium to be treated here are heavy metal cations, especially Ca ²⁺ .

The use of the treating agents according to the invention is advantageous in that heavy metal cations can be removed very efficiently, especially over a wide range of pH, generally from 7 to 12.

Further, it can be seen that the treated form of the present invention to which the precipitate form after separation, that is, the heavy metal is added, has excellent stabilizing (immobilizing) ability. The treatment agent of the present invention shows very good behavior against leaching. That is, the treating agent of the present invention, when placed in a location where water is present, releases virtually no or almost no heavy metal cations. The amount of heavy metal cations in the leachate obtained by known leach test methods is very small.

Therefore, another subject of the present invention is a treating agent for stabilizing (immobilizing) heavy metal cations contained in a medium, characterized in that it contains at least one kind of treating agent described above.

The presence of the carrier during the treatment of the present invention causes local sedimentation around the periphery of the carrier, but surprisingly, it has been found that the carrier accelerates the sedimentation, and particularly increases the sedimentation speed in the case of clay. . Similarly, the carrier, as described above, allows the content of heavy metal cations in the leachate to be reduced to a very small amount.

The following examples illustrate the present invention but should not be construed as limiting.

The sodium silicate of Example 1 -SiO ₂ / Na ₂ O molar ratio of 1, 0.21 mol / at a concentration of silicate expressed in SiO _2, and an aqueous solution 400ml of pH 13, the Na ₂ CO ₃ of -8.84g An aqueous solution of sodium carbonate, which was obtained by dissolving in 400 ml of water and was adjusted to pH 13 with sodium hydroxide in advance, was mixed.

After stirring, the solution of this mixture was dried with a Buchi type atomizer.

Flow rate is 20ml / min, inlet temperature is 240 ℃, outlet temperature is 110 ℃
Set to.

The product contains sodium silicate and sodium carbonate,
Its CO ₃ ^2- / SiO ₂ molar ratio was 1, and its water content was 7% by weight.

Example ₂ -SiO 2 / Na 2 O molar ratio of the sodium silicate 3.3 to 0.2 mol / at a concentration of silicate expressed in SiO _2, and an aqueous solution 657.5ml of pH 12.5, Na of -139.5G ₂ An aqueous solution of sodium carbonate, obtained by dissolving CO ₃ in 600 ml of water, previously adjusted to pH 12.5 with sodium hydroxide and adjusted to a volume of 657.5 ml by adding water, was mixed.

After stirring, the solution of this mixture was dried with a Buchi type atomizer.

Flow rate 20ml / min, inlet temperature 235 ° C, outlet temperature 120 ° C
Set to.

The product contains sodium silicate and sodium carbonate,
Its CO ₃ ^2- / SiO ₂ molar ratio was 1, and its water content was 10% by weight.

The sodium silicate of Example 3 -SiO ₂ / Na ₂ O molar ratio of 1, 0.21 mol / at a concentration of silicate expressed in SiO _2, and an aqueous solution 400ml of pH 13, the Na ₂ CO ₃ of -8.84g An aqueous solution of sodium carbonate, which was obtained by dissolving in 400 ml of water and was adjusted to pH 13 with sodium hydroxide in advance, was mixed.

 The solution of this mixture was stirred.

With stirring, 75 g of montmorillonite clay was added to this.

 Stirring was continued for 15 minutes.

The obtained suspension was dried with a Buchi type atomizer.

Flow rate 10ml / min, inlet temperature 240 ° C, outlet temperature 130 ° C
Set to.

The product contains sodium silicate, sodium carbonate and montmorillonite, the CO ₃ ^2- / SiO ₂ molar ratio of which is 1,
Montmorillonite clay is 75% by weight and has a moisture content of 6%.
% By weight.

Example 4 18 mg of the product prepared in Example 1 were added with stirring to 100 ml of a CuCl ₂ solution having a Cu ²⁺ concentration of 48 mg /. This amount corresponds to a (SiO ₂ + CO ₃ ^2- ) / Cu ²⁺ molar ratio of about 2.1.
Stirring continued for 30 minutes.

 The pH of the resulting suspension was 9.7.

 The suspension was then left at room temperature for 4 hours.

 This was then centrifuged at 3000 times / min for 5 minutes.

The supernatant liquid had a Cu ^{+ 2} concentration of less than 2 mg / by atomic absorption spectrometry.

The product 18mg prepared in Example 5 Example 1 was added with stirring to ZnSO ₄ solution 100ml with Zn ²⁺ concentration of 51 mg /. This amount corresponds to a (SiO ₂ + CO ₃ ^2- ) / Zn ²⁺ molar ratio of about 1.8.
Stirring continued for 30 minutes.

 The pH of the resulting suspension was 8.2.

 The suspension was then left at room temperature for 4 hours.

 This was then centrifuged at 3000 times / min for 5 minutes.

The supernatant liquid had a Zn ^{+ 2} concentration of less than 1.5 mg / by atomic absorption spectrometry.

Example 6 18 mg of the product prepared in Example 1 were added with stirring to 100 ml of a CdCl ₂ solution having a Cd ²⁺ concentration of 51 mg /. This amount corresponds to a (SiO ₂ + CO ₃ ^2- ) / Cd ²⁺ molar ratio of about 1.8.
Stirring continued for 30 minutes.

 The pH of the resulting suspension was 10.

 The suspension was then left at room temperature for 4 hours.

 This was then centrifuged at 3000 times / min for 5 minutes.

The supernatant liquid had a Cd ⁺² concentration of less than 0.5 mg / by atomic absorption spectrometry.

Example 7 An aqueous effluent containing Fe ³⁺ , Al ³⁺ , Ca ²⁺ , Zn ²⁺ , Pb ²⁺ and Cd ²⁺ was prepared as follows.

 The following volumes were dissolved in one liter of 0.0M hydrochloric acid.

It was _{CaCl 2 · 2H 2 O 7.33g FeCl} 3 · 6H 2 O 0.483g AlCl 3 · 6H 2 O 0.994g ZnCl 2 3.12g PbCl 2 0.737g 3CdSO 4 · 8H 2 O 0.069g Water to make 2 l.

 The pH of the obtained effluent was 1.3.

 The effluent has the following concentrations expressed in mg / mg:

Ca ²⁺ 1070 Al ³⁺ 52.8 Fe ³⁺ 50.9 Zn ²⁺ 712 Pb ²⁺ 274 Cd ²⁺ 5 1.745 g of the treating agent prepared in Example 1 was introduced into 250 Ml of the above effluent with stirring, and stirred. For 30 minutes.

 The pH of the resulting suspension was 9.2.

 The suspension was then left at room temperature for 4 hours.

 This was then centrifuged at 3000 times / min for 10 minutes.

The concentrations of Fe ³⁺ , Al ³⁺ , Ca ²⁺ , Zn ²⁺ , Pb ²⁺ and Cd ^{2+ in} the supernatant were as follows.

Ca ²⁺ 85 Al ³⁺ Less than 0.1 Fe ³⁺ Less than 0.1 Zn ²⁺ 1 Pb ²⁺ Less than 0.01 Cd ²⁺ 0.07 Example 8 7.282 g of the product prepared in Example 2 was added at a Zn ²⁺ concentration of 1 g /
ZnCl ₂ solution ^{_{((SiO 2 + CO 3 2-}} ) / Zn 2+ corresponding to a molar ratio of about 1.9) was added with stirring to a 2 liter, 30 stirring
Continued for minutes.

 The pH of the resulting suspension was 9.35.

 The suspension was then left at room temperature for 4 hours.

 This was then centrifuged at 3000 times / min for 5 minutes.

The supernatant had a Zn ²⁺ concentration of 0.2 mg / by atomic absorption spectrometry.

 The precipitate was dried at room temperature. Its weight was 8.36 g.

32 ml of water was added to 2 g of this precipitate and the suspension was stirred.

 The pH was adjusted to 7 by adding 1.4 ml of 0.5N acetic acid solution.

 The volume was made up to 40 ml by adding water.

 Then the suspension was stirred for 20 hours and filtered.

The solid-liquid contained Zn ²⁺ 5.5 mg /. Thus, the precipitate is hardly leachable.

Example 9 1.728 g of the product prepared in Example 2 was mixed with a Pb ²⁺ concentration of 1 g /
Is added to 2 liters of a PbCl ₂ solution (corresponding to a molar ratio of (SiO ₂ + CO ₃ ²⁻ ) / Pb ^{2+ of} about 1.4) with stirring, and stirring is continued for 30 minutes.
Continued for minutes.

 The pH of the resulting suspension was 9.5.

 The suspension was then left at room temperature for 4 hours.

 This was then centrifuged at 3000 times / min for 10 minutes.

The supernatant had a Pb2 ⁺ concentration of 0.1 mg / Ag by atomic absorption spectrometry.

 The precipitate was dried at room temperature. Its weight was 2.23 g.

24 ml of water was added to 1.5 g of this precipitate and the suspension was stirred.

 The pH was adjusted to 7 by adding 0.1 ml of 0.5N acetic acid solution.

 The volume was made up to 30 ml with water.

 Then the suspension was stirred for 20 hours and filtered.

The filtrate contained 2 mg / Pb ²⁺ . Thus, the precipitate is hardly leachable.

Example 10 80 mg of the product prepared in Example 3 was treated with a Cu ²⁺ concentration of 50 mg /
Was added with stirring to 100 ml of a CuCl ₂ solution (corresponding to a (SiO ₂ + CO ₃ ²⁻ ) / Cu ²⁺ molar ratio of about 1.7) and stirring was continued for 30 minutes.

0.1 ml of 0.5N hydrochloric acid was added to the resulting suspension to adjust the pH to 8.
I made it.

 The suspension was then left at room temperature for 4 hours.

 This was then centrifuged at 3000 times / min for 5 minutes.

The supernatant liquid had a Cu ²⁺ concentration of less than 0.2 mg / by atomic absorption spectrometry.

Example 11 80 mg of the product prepared in Example 3 was used at a Cu ²⁺ concentration of 50 mg /
Was added with stirring to 100 ml of a CuCl ₂ solution (corresponding to a (SiO ₂ + CO ₃ ²⁻ ) / Cu ²⁺ molar ratio of about 1.7) and stirring was continued for 30 minutes.

The pH of the resulting suspension was adjusted to 12 by adding 0.5 ml of 1N hydrochloric acid.

 The suspension was then left at room temperature for 4 hours.

 This was then centrifuged at 3000 times / min for 5 minutes.

The supernatant had a Cu ²⁺ concentration of less than 2 mg / by atomic absorption spectrometry.

Example 12 75 g of montmorillonite is an aqueous solution of sodium silicate in a SiO ₂ / Na ₂ O molar ratio, wherein the silicate concentration represented by SiO ₂ is
0.2 mol / of 830 ml was added with stirring.

 Stirring was continued for 15 minutes.

The obtained suspension was finally dried with a Buchi type atomizer.

Flow rate is 10ml / min, inlet temperature 240 ° C, outlet temperature 135
Set to ° C.

The resulting product contained sodium silicate and 72% by weight of montmorillonite clay and 9% by weight of water.

Example 13 The products prepared in Examples 1, 3 (inventive) and Example 12 (not inventive) were combined with a heavy metal cation (in this example,
The settling velocities when used for purification of CU ²⁺ ) were compared.

(1) 180 mg of the product produced in Example 1 was mixed with 500 ml / C
Introduce into 100 ml of CuCl ₂ solution with u2 ⁺ concentration, add 0.5N hydrochloric acid
0.5 ml was added to bring the pH to 8.

(2) 803 mg of the product prepared in Example 3 was added to 500 ml / C
Introduce into 100 ml of CuCl ₂ solution with u2 ⁺ concentration, add 0.5N hydrochloric acid
The pH was brought to 8 by adding 1.5 ml.

(3) 803 mg of the product prepared in Example 12 is mixed with 500 ml / Cu ²⁺
Introduce into 100 ml of CuCl ₂ solution with concentration, 3 ml of 0.5N hydrochloric acid
Was added to bring the pH to 8.

After stirring for 1 minute, each of the suspensions obtained in the above (1), (2) and (3) was poured into a measuring cylinder.

The settling velocities were compared. The following table shows the total clarified volume (ml) at each time point (min) during sedimentation for each product prepared in Examples 1, 3, and 12.

Product of Example 3 (silicate / carbonate / clay composite)
Is the fastest sedimentation speed obtained.

The sedimentation rate obtained with the non-inventive product obtained according to Example 12 is the slowest.

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁷ , DB name) C02F 1/28 B01J 20/16

Claims (13)

(57) [Claims] 1. An at least one compound A comprising an alkali metal silicate or an aluminosilicate, and at least one compound B comprising an alkali metal carbonate or a hydroxycarbonate selected from hydrotalcite and dawsonite. A scavenger for removing heavy metal cations contained in a medium, comprising: 2. The scavenger according to claim 1, wherein the compound A is sodium silicate or potassium silicate. 3. Compound A has a SiO ₂ / Na ₂ O molar ratio of 0.5 to 3.8.
The scavenger according to claim 2, which is sodium silicate. 4. The scavenger according to claim 1, wherein compound B is an alkali metal carbonate. 5. The compound according to claim 4, wherein the compound B is sodium carbonate.
Scavenger. 6. The compound A / compound B has a molar ratio of CO ₃ ^2- / SiO ₂
The scavenger according to any one of claims 1 to 5, wherein the molar ratio is 0.05 to 10. 7. The scavenger according to claim 1, further comprising at least one carrier made of clay. 8. The capturing agent according to claim 7, wherein the content of the carrier is 10 to 90% by weight. 9. The method according to claim 7, wherein the clay is a natural product or a synthetic product.
Or 8 scavengers. 10. The scavenger according to claim 7, wherein the clay is montmorillonite. 11. The scavenger according to claim 1, wherein the weight average particle diameter is 15 to 100 μm. 12. The method according to claim 1, wherein the medium is an aqueous effluent.
11 scavengers. 13. The scavenger of claim 12, wherein the aqueous effluent is water obtained from the washing of waste incineration fumes.